All this means is someone has your email address, which is to be expected. It doesn't mean someone is impersonating you so no panic is required.
I would check some of the other emails to see if the source is the same. If so it may be that your form uses your email address - it needs something otherwise the email is not valid.

When I checked some of the other emails, I found my address as the sender in all of them. I guess it has been all along, but I'd been looking more carefully at everything with all the Heartbleed chatter!